HID Light Guide

Discussion in 'Growing Marijuana Indoors' started by BalladBlack, Nov 27, 2009.

  1. High intensity discharge grow lights (HID)
    HID lighting systems have made the dream of year round gardening a reality for tens of thousands of indoor gardeners and commercial greenhouse growers worldwide. Thanks to their incredible efficiency (up to 10x more lumens per watt than incandescent bulbs) and a color spectrum that plants love, indoor growers are able to achieve incredible results year round.

    HID lighting is used worldwide by commercial growers
    HID grow lights provide many benefits that are otherwise unattainable with conventional fluorescent and incandescent lamps. Supplemental HID lighting enables commercial growers to increase crop yields, and produce crops entirely out of season which can be very rewarding. HID lighting is so efficient and powerful that many indoor growers benefit from its use year round. HID lights are powered by standard 110-120VAC wall current and use a regular three prong plugs to connect.

    Picture of a ballast, reflector, and bulb.

    A primer on photosynthesis
    Plants have the unique ability to manufacture their own food. In the process known as photosynthesis, chlorophyll uses light energy to convert carbon dioxide from the air and water from the ground into food sugar. When these elements abound in a perfect environment, the production of food is limited only by factors that effect photosynthesis, being the intensity, color and duration of the daily light the plant receives.

    The chart below shows the relationship between chlorophyll activity and color of light. Common electric light sources are indicated on the chart. You will notice that Metal Halide (MH) and High Pressure Sodium (HPS) produce light in the most photosynthetically active spectrums.


    As the chart indicates, cool (blue) and warm (orange) colors in the spectrum enhance chlorophyll activity and food production. Cool light is most pronounced during the summer months when the sun is highest in the sky. It is responsible for keeping plants growth compact and shapely. Warm light, such as when the sun is lower in the sky during the fall harvest months, is responsible for triggering reproduction in plants in the form of flowers and fruits.

    Thus, when vegetating your plants, your best bet is an MH lighting system. If you want to flower plants, the HPS lamp is your best bet. As a matter of fact, there are conversion bulbs which allow you to buy one type of system and use both types of lamps. Conversion bulbs cost more but give you the added benefit of being able to start your plants with the MH bulb, ensuring tight, compact growth, and then switching over to the HPS lamp when the plants are ready to fruit and flower for higher yield. The latest breakthrough is in switchable ballasts which can use standard MH and HPS bulbs.

    Metal Halide (MH)
    lamps emit primarily
    blue light making them
    ideal for the vegetative
    growth stage.


    High Pressure Sodium (HPS)
    lamps emit primarily red light
    which causes exaggerated
    flowering and fruiting during
    the plant reproductive stage.

    The primary benefit to employing a High Intensity Discharge (HID) horticultural lighting system is the control it gives you over your plant's growing environment. In many areas, once fall arrives the growing season is over, and if you're a hard-core gardener like us, you'll miss it dearly! Horticultural lighting systems allow us all to extend the growing season by providing our favorite plants with an indoor equivalent to sunlight. This is a great advantage for those of us who appreciate having a year-round supply of fresh herbs! HID lighting is also great way to jump-start spring by starting your seedlings months ahead of last frost for outdoor growers.

    Sizes of grow lights
    MH and HPS grow lights come in the following Watt sizes; 50W, 100W, 150W, 175W, 250W, 400W, 600W,1000W and 1500W.A general rule of thumb for selecting the correct wattage grow light is to determine the size and shape of your garden area. Since grow lights emit a relatively square pattern of light, it is best to consider each light as covering a square of garden. Here is a list of the coverage each size grow light will provide.
    50W = 1.5' x 1.5'
    100W = 2' x 2'
    250W = 3' x 3'
    400W = 4' x 4'
    600W = 5' x 5'
    1000W = 6' x 6'
    1500W = 8' x 8'
    Another great advantage of indoor horticultural lighting is your ability to control the length of daylight thus empowering you with the ability to force flower your favorite strain even when completely out of season. Remember, to grow perfect plants, the secret to the right light is Color, Intensity and Duration!

  2. A quick nutshell description of lighting types to give some contrast and basic information as well.

    Incandescent – Incandescent lamps have relatively short lives (typically 1000 to 2000 hours of use) and a re the least efficient of common light sources. In fact, only about 15 percent of the energy they use comes out as light – the rest becomes heat. However, they produce a pleasant color that is similar to natural sunlight. Incandescent lamps are the least expensive to buy but the most expensive to operate. Reduced-wattage incandescents produce about the same light output but consume less energy than standard bulbs.

    Tungsten-halogen – Halogen lamps are a type of incandescent lamp that has become increasingly popular in recent years. They produce a whiter, more intense light than standard incandescent and are typically used for decorative, display or accent lighting. Halogen spotlights also have good focusing ability in small areas. They are about twice as efficient as regular incandescent lamps and last two to four times longer than most incandescent lamps.

    Compact Fluorescent Lamps – Compact fluorescent lamps (CFLs) are similar in operation to standard fluorescent lamps but are manufactured to produce colors similar to incandescent lamps. They are available in a range of types and sizes to meet most applications including downlighting, ambience, task and general space lighting. CFLs are about four times as efficient as incandescents and last up to 10 times longer. Lamp ballast combinations that replace incandescents in standard fixtures are substantially more expensive than their incandescent counterparts.

    Tubular fluorescent fixtures – Tubular fluorescent lamps are one of the most common sources of commercial lighting and also are among the most efficient. The new generation of small diameter lamps (T-8 and T-10) is particularly efficient. It is important to understand that lamps and ballasts work as a system and the overall efficiency of a lighting fixture is dependent on the lamp/ballast combination. Traditional magnetic ballasts are less efficient than modern electronic ballasts. All ballasts are now required by the government to meet minimum efficiency standards. Fluorescent lamps last up to 20,000 hours of use.

    High-intensity discharge (HID) – This category of high output light sources that includes mercury vapor, metal halide, high-pressure sodium and low-pressure sodium lighting. As with fluorescent lights, HID lights require a ballast for proper lamp operation. The efficiency of HID sources varies widely from mercury vapor ¡V with an efficiency almost as low as incandescent - to low-pressure sodium which is among the most efficient light sources. Color rendering varies widely from the bluish cast of mercury vapor lamps to the distinctly yellow light of low-pressure sodium.

    The Cost to Run a Lighting System
    To get the operating cost per hour for a light, take the lights combined wattage, and divide it by 1000 to get the kilowatts used. Then multiply that number by the amount your electric company charges per kilowatt hour. HID lights will use the number of watts it emits per hour, ie; 600w system will use 600 watts per hour (regardless of spectrum).
    (light wattage output / 1000) x electricity cost per kilowatt hour = Operating cost per hour
    operating cost per hour x hours used per month = Operating cost per month

    Distance to hang HID lights from plants:
    This is very important because too close can easily burn plants, cause soil to dry very fast, and so on. Distance also varies on if you are using air - or water - cooled and wether your lights are using light movers. Consider the numbers below as a basic guide, and always raise the lights if you see any signs of heat damage to plants.

    1.000 watts: 16-24 inches
    600 watts: 14-20 inches
    400 watts: 12-18 inches
    250 watts: 8-14 inches

    A rough average of distance to plants. Keep in mind some can go outside these parameters depending on several variables as listed previously.

    How much light do I need?
    This is a tricky answer, and no two people will agree exactly. However,
    every experienced grower will agree that you'll need more than you think.
    Cannabis loves light. Some general rules that often get passed around:

    1. At least 100 watts of light per plant, or
    2. At least 35 watts of light per square foot of plant

    A very rough approximation of the wattage needed for a given number of
    moderately sized (3-4 ft tall) plants is:

    1-2 plants: 250 watts
    3-4 plants: 400 watts
    5-6 plants: 600 watt
    7-10 plants: 1000 watts

    The more you can spread the light between multiple bulbs the better. In
    other words, it is to better to light your closet with 3x400watt bulbs than
    either a 1x1000watt bulb or even 2x600 watt bulbs.
  3. Exactly what I was looking for. Thank you!

    I've read that some people skip the MH stage completely and just use HPS throughout the entire grow cycle. Could you comment on this?
  4. Many growers will use the Metal Halide spectrum for vegetative growth and switch to HPS for the flowering cycle. In recent years switchable ballasts have been introduced, which allow you to run a HPS or Metal Halide bulb off of the same ballast.

    An HPS does not put out the best spectrum for vegging. I suppose I can see running a HPS for a 12/12 grow, but just get a switchable ballast and conversion bulb. Even running a 12/12 grow the plant will not start showing sex until it is mature enough to do so. Roughly 25-45 days depending on so many variables.

    I would recommend just using both bulb type types if possible to maximize yield. You won't be dissapointed with a large plant full of buds.
  5. Re: 600W = 5' x 5', 5-6 plants: 600 watt

    That doesn't make any sense to me. How about 10,000 lumens per plant
  6. If you have a switchable ballast you don't need a conversion bulb. Just the correct wattage bulb.
  7. yea thats what i was thinking
  8. Oh damn, just noticed that lol. Sorry, when I checked the forum earlier I was baked. My bad.

    Also I put this together to help learn, I am still learning myself. Maybe I shouldn't have tried to make a guide when I was still learning. Just thought it would be nice to get the information in one spot.
  9. Nothing wrong with that. I've seen that before posted recently here. I'm doing 9 in about a month under 600w HPS at 95,000 lumens. I should be able to do that although "some" of that "info" seems to disagree with that. :D
  10. Lol, see what I mean?:D
  11. good guide. answered a lot of questions i had.
  12. Glad I could help.:wave:
  13. Because this got some good attention in another thread, I figure I'll place it in here as it was helpful to some.

    "It's been established for many many many years now that cannabis is a C3 plant. It does not need a dark period.

    C3 plants gather CO2 only during the light period when they are photosynthesizing. As long as the light is on, C3 plants gather and use CO2 for photosynthesis.

    Some growers practice a version of anthropomorphism with their plants. They believe that since people need rest, plants do as well. Concerning cannabis, this is not true.

    Every grower can make a personal choice about light cycle. They can save on their electric bill or prolong ballast/bulb life. 18/6 can be less of a "shock" when changing over to 12/12 for flowering than 24/0 or heat issues can be addressed by fewer hours of light, but basic botany has proven long ago that cannabis needs no dark period.

    Ed Rosenthal, Mel Frank and Robert Clarke all have covered this extensively over their careers.

    hXXp://www.mellowgold.com/grow/mjbotany-removed/marijuanabotany1.html Marijuana Botany Chapter 1 - Sinsemilla Life Cycle of Cannabis
    hXXp://www.cannabisculture.com/articles/3127.html Need the dark

    Marijuana plants photosynthesize as long as they receive light as well as water, air, nutrients and suitable temperature. Photosynthesis is the process in which plants use the energy from light (primarily in the blue and red spectrum's) to combine carbon dioxide (CO2) from the air and water (H2O) to make sugar while releasing oxygen to the air.

    Plants use sugars continuously to fuel metabolic processes (living) as well as for tissue building. The plant combines nitrogen (N) with the sugar to make amino acids, the building blocks of proteins. They are the substance of plant tissue. When the light is off, the plant's metabolic processes, respiration and growth, continue.

    The plant can photosynthesize continuously so it produces the most energy and growth when the light is on, continuously. Continuous light does not stress the plant, which reacts somewhat mechanistically to it.

    Plants under an 18-6 light-dark regimen are producing sugar only three quarters of the time. They are thus growing at only 75% of their potential. Leaving the light on continuously will result in bigger plants, faster, which leads to higher yields.

    Cannabis is a light demanding plant. Professional growers keep the light on their plants using the 24/0 photoperiod for this reason. Plants that grow under 24/0 flourish and do not need a quantity of darkness in order to rest and perform photosynthesis properly. Plants that are grown in optimal conditions under 24/0 light regime grow vigorusly and the benefits of a 24/0 photoperiod can be seen actively in the results. More nodes are formed, more branches are created, leaf numbers increase, the plant is growing at its finest.

    Some growers opt to use 18/6 as their photoperiod. This is 18 hours of light, six hours of darkness light regime. Under these conditions the plant will grow quite naturally but not as vigorously as the 24/0 photoperiod.

    The 18/6 photoperiod expels 3/4 the amount of light that a 24/0 photoperiod does. Although this does not mean that a plant produces 1/4 less leaves,branches and nodes under the 18/6 photoperiod, it certainly does show the correlation between light and cannabis growth. As we have said already, cannabis is a light demanding plant. There are no problems associated with 24/0 and although some have attributed cannabis sexual dysfunction (the hermaphrodite conditon) to 18/6 photoperiod these problems are actually the result of heat stress.

    A 24/0 photoperiod requires that your grow room temperature be kept well monitored. The 18/6 option is cheaper to run. You use a quarter less electricity and this will have an impact on your electricity bill. Also the 18/6 photoperiod will generally extend the bulb's lifespan. During the 6 hours of darkness the grow room is allowed to cool down for this period but a well maintained good grow room setup should not require a cooling down period.

    24/0 and 18/6 both share the same problem though. Once you start the photoperiod you should keep that way especially when the plants near maturity (the preflowering stage). An irregular photoperiod can cause more males than females to develop. It can also cause sexual dysfunction to appear. Whether you choose 24/0 or 18/6 as your vegetative photoperiod try to keep that photoperiod unitl your plants are mature enough to express their sex.

    C3 plants can photosynthesize all day if they have light and a high enough level of CO2, whereas C4 plants store the CO2 during the night, and use it during the day. This is why photosynthesis decreases near the end of the day in C4 plants, they've run low on CO2."
    -My original post in Buthidae's Journal.

    "C3 plants can have problems with photorespiration if the conditions become too dry, or too hot, as they then lose CO2 and photosynthesis as well as growth slows. The dark period in C3 plants appears to contribute to growth because this is when they will typically stretch. C3 plants under 24 hr light will usually be shorter and bushier, and root growth may also be less vigorous, but only because it doesn't need to be. As long as a C3 plant has access to plenty of water, nutrients, and light (while maintaining a moderate temperature and humidity), photosynthesis will continue at an accelerated rate."
    -Follow up by Buthidae
  14. #15 BalladBlack, Nov 29, 2009
    Last edited by a moderator: Dec 5, 2009
    Light Distance Charts

    Attached Files:

  15. Added a couple charts for reference.
  16. very usefull guide. i noticed that you said its better to use 3x400watt then 2x600 so its better to use 4x250watt to have even coverage?

    i want to have a veg room with mh? and a flower room with hps?. i have a window in my 2 car garage so fresh air comes with co2 thro the window?

    also how come we dont hear much of lps?

    i will be living in the garage so out of my 12x12x8ft tall garage what can i work with? i will get all needed items to yeild as much as possible and as quick as possible.

    first time so i dont think i will go with hydro but if its simple to understand why not
  17. mmm this is a really informing thread very nice, i loved the charts too this should help a ton of people :)
  18. Great charts and nice guide man,

  19. #20 dgaf813x, Apr 12, 2010
    Last edited by a moderator: Apr 12, 2010

    My question on this is the 3x400watt hps doesnt mean youll get the same amount of lumens as the 2x600watt hps, but im actually using this formula for my 3'x2' box with 5x70watt hps and i thought i was doing this, in a sense, wrong because it doesnt have the same amount of lumens as maybe a 400watt. Not even close actually, but referring to your quote could this actually be a better option? i know its only 350watts so of course its not the same as a 400watt. Am i correct in my thinking?

    To make up for some lost lumens i did add 7x23watt cfl's.

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